The present invention relates to a mercury-free manganese dry battery and more specifically to an improvement in discharge performance of the manganese dry battery.
Mercury has mainly been used as a corrosion inhibitor of the zinc anode can in manganese dry batteries. In this case, mercury is included in the separator and incorporated in the battery. The separator is obtained by applying a sizing agent on a separator base sheet and drying it, where the pasting agent is provided by dissolving starch and a binder in an alcohol solvent. The cathode mixture is covered with the separator and charged in the zinc anode can. Mercury of several % by weight has generally been added to the pasting agent, which is applied on the separator. When in close contact of the separator with the inner surface of the zinc can, an amalgam is formed on the surface of the zinc can and thus effectively prevents corrosion of the zinc can.
From the viewpoint of the environmental protection, a variety of mercury-free dry batteries have been developed and proposed: for example, one using a zinc alloy of high corrosion resistance (for example, JAPANESE PATENT LAID-OPEN GAZETTE No. 6-196155) and one with an anti-corrosive additive (for example, JAPANESE PATENT LAID-OPEN GAZETTE No. 4-10357).
When a mercury-free manganese dry battery is discharged under a specific loading resistance, the discharge capacity may be lowered extremely. This phenomenon specifically occurs in the course of discharge under,light loading conditions.
The extreme decrease in discharge capacity may be ascribed to an abrupt increase in internal resistance of the battery in the course of discharge in the case where the manganese dry battery is discharged at the resistance of light loading.; The abrupt increase leads to an abrupt drop of the closed path voltage in the course of discharge under light loading conditions.
One possible means to prevent the increase in internal resistance is to increase the amount of electrolyte solution in the cathode mixture or in the pasting agent of the separator, or alternatively increase the amount of carbon used as the conductive material in the cathode mixture. These methods, however, decrease the amount of manganese dioxide in the cathode mixture and thereby deteriorate the overall discharge performance of the batteries including the discharge performance under the heavy loading conditions.
The object of the present invention is to solve the above problems and to provide a mercury-free manganese dry battery that prevents an increase in internal resistance in the course of discharge and has excellent discharge properties especially under light loading conditions.
While the novel features of the invention are set forth particularly in the appended claims, the invention, both as to organization and content, will be better understood and appreciated, along with other objects and features thereof, from the following detailed description taken in conjunction with the drawings.